The present invention relates to a technique that carries out bidirectional, reciprocating main scan to print an image on a printing medium. More specifically the present invention pertains to a technique that adjusts misalignment of dot recording positions in a main scanning direction between a forward pass and a backward pass of the main scan.
Recently color printers having a print head that ejects a plurality of different color inks have been widely used as an output device of computers. Some of such color printers have the function of xe2x80x9cbidirectional printingxe2x80x9d for enhancing the printing speed.
In bidirectional printing, misalignment of recording positions in a main scanning direction on a forward pass and a backward pass of main scan often arises due to a backlash of a driving mechanism in the main scanning direction or a warp of a platen that supports a printing medium. One of the techniques proposed to relieve such positional misalignment is disclosed in JPA 5-69625 filed by the applicant of the present invention. This prior art technique registers in advance a potential amount of positional misalignment (deviation in printing) in the main scanning direction and corrects the dot recording positions on the forward pass and on the backward pass, based on the registered amount of positional misalignment.
The print head of the printer generally has a nozzle array that includes a large number of nozzles arranged in a sub-scanning direction. When the print head is driven in the main scanning direction, mechanical vibrations may occur on the print head to slightly shift the orientation of the nozzle array from the sub-scanning direction. Furthermore, the nozzle array may be slightly inclined to different orientations on the forward pass and on the backward pass, for example, due to the backlash of the driving mechanism in the main scanning direction. In such cases, it is difficult to accurately determine the amount of potential positional misalignment, since the nozzle array does not move back and forth keeping the specified posture perpendicular to the main scanning direction as a whole.
The object of the present invention is to solve the problem of the prior art technique discussed above and accordingly to provide a technique that relieves positional misalignment in the main scanning direction on a forward pass and a backward pass of main scan with regard to a nozzle array in a printing apparatus of bidirectional printing.
In order to attain at least part of the above and the other related objects, the present invention is directed to a printing apparatus that comprises a print head having a nozzle array, which is arranged in a sub-scanning direction and ejects ink droplets to record dots on a printing medium, and carries out bidirectional, reciprocating main scan to complete printing on the printing medium. With this printing apparatus, a positional misalignment test pattern is printed on the printing medium with a representative nozzle sub-array, which is part of the nozzle array and is within a predetermined range around a center of the nozzle array. Then a correction value is determined according to correction information that represents a favorable correction state selected based on the positional misalignment test pattern, where the correction value is used to correct the misalignment of recording positions in the main scanning direction on the forward pass and the backward pass of the main scan. The misalignment of recording positions in the main scanning direction is actually corrected with the correction value thus determined in the course of bidirectional printing. Here xe2x80x9cthe representative nozzle sub-array that is within a predetermined range around a center of the nozzle arrayxe2x80x9d represents a group of plural nozzles that includes a specific nozzle closest to the center position along the length of the nozzle array and does not include end nozzles on either end of the nozzle array.
In the case where the angle of the nozzle array in the main scanning direction on the forward pass is slightly different from that on the backward pass, a correction value determined using a nozzle on one end of the nozzle array would cause a significant misalignment of recording positions of ink droplets with regard to the nozzles on the other end of the nozzle array. The arrangement of the present invention determines the correction value on the basis of the nozzles in the neighborhood of the center of the nozzle array. Accordingly, it reduces the total misalignment of dot recording positions, due to the variation in the angle of the nozzle array. The technique of the invention determines the correction value according to the correction information which represents the favorable correction state selected based on the positional misalignment test pattern printed with the representative nozzle sub-array. The correction value is determined not on the basis of deductive inference but on the basis of the positional misalignment test pattern actually printed on a printing medium. The correction value can thus be determined adequately to relieve the actual printing misalignment.
The nozzle array preferably comprises: a color nozzle array including a plurality of color nozzles to eject color ink that are arranged in a predetermined sequence in the sub-scanning direction; and a black nozzle array including a plurality of black nozzles to eject black ink that are arranged in a predetermined sequence in the sub-scanning direction. In this application, a memory included in the printing apparatus stores a first correction value and a second correction value therein. The first correction value is set for correcting the positional misalignment of recording positions in the main scanning direction on the forward pass and the backward pass of the main scan with regard to a representative color nozzle sub-array, which is part of the color nozzle array and is within a predetermined range around a center of the color nozzle array. The second correction value is set for correcting the positional misalignment of recording positions in the main scanning direction on the forward pass and the backward pass of the main scan with regard to a representative black nozzle sub-array, which is part of the black nozzle array and is within a predetermined range around a center of the black nozzle array. Here the color nozzle array and the black nozzle array may have any positional relationship.
This arrangement corrects the misalignment of recording positions in the course of bidirectional printing with the first correction value, which reflects the characteristics of the color nozzle array, and with the second correction value, which reflects the characteristics of the black nozzle array. Namely the arrangement of using both the first correction value and the second correction value can reflect the characteristics of the color nozzle array and the black nozzle array on the correction of the misalignment of recording positions in the course of bidirectional printing.
The positional misalignment correction unit may correct the misalignment of recording positions in the main scanning direction in the course of bidirectional printing with regard to the nozzle array with a mean value of the first correction value and the second correction value. This arrangement readily corrects the misalignment of recording positions in the course of bidirectional printing by taking into account both the color nozzle array and the black nozzle array.
It is preferable that the positional misalignment correction unit corrects the misalignment of recording positions with the first correction value in a print mode that the nozzles of the color nozzle array are used. In the case of color printing, this arrangement carries out the correction with the first correction value that reflects the characteristics of the color nozzle array. This accordingly ensures the correction of recording positions suitable for color printing.
It is also preferable that the positional misalignment correction unit corrects the misalignment of recording positions with the second correction value in a print mode that the nozzles of the color nozzle array are not used. In the case of monochromatic printing, this arrangement carries out the correction with the second correction value that reflects the characteristics of the black nozzle array. This accordingly ensures the correction of recording positions suitable for monochromatic printing.
The positional misalignment correction unit may correct the misalignment of recording positions with the first correction value with regard to the color nozzle array, and corrects the misalignment of recording positions with the second correction value with regard to the black nozzle array. This arrangement ensures the optimum corrections for both the color nozzle array and the black nozzle array in the process of one printing operation.
It is preferable that the color nozzle array includes yellow nozzles for ejecting yellow ink, cyan nozzles for ejecting cyan ink, and magenta nozzles for ejecting magenta ink, and that the representative color nozzle sub-array consists of either of cyan nozzles and magenta nozzles.
In the arrangement of determining the correction value on the basis of the representative nozzle sub-array that is within the predetermined range in the neighborhood of the center of the nozzle array, the nozzles in the neighborhood of both the ends of the nozzle array have a greater degree of misalignment of dot recording positions in the main scanning direction than the nozzles in the neighborhood of the center of the nozzle array. Among yellow, cyan, and magenta, the misalignment of recording positions in yellow is least conspicuous. The misalignment of recording positions in magenta and cyan is more conspicuous than that in. yellow. In this preferable structure, the cyan nozzles or the magenta nozzles are arranged in the neighborhood of the center of the nozzle array and the correction value is determined with either the cyan nozzles or the magenta nozzles as the representative color nozzle sub-array. This arrangement makes the total misalignment of recording positions of dots sufficiently inconspicuous.
The present invention is realized by a diversity of applications as given below:
(1) Bidirectional printing apparatus;
(2) Method of bidirectional printing;
(3) Method of correcting misalignment of recording positions in the course of bidirectional printing;
(4) Computer programs to attain any of the above apparatus and methods;
(5) Recording media in which computer programs to attain any of the above apparatus and methods is recorded; and
(6) Data signals that include computer programs to attain any of the above apparatus and methods and are embodied in carrier waves.